2D spatial-variant phase errors compensation for ISAR imagery based on contrast maximisation

Range and azimuth spatial-variant phase errors are usually presented in high-resolution inverse synthetic aperture radar imagery as the manoeuvring motion of the observed targets. It could not be effectively compensated by the traditional autofocus algorithms. A new method is proposed for 2D spatial-variant phase errors compensation based on contrast maximisation. First, a novel phase error parametrical signal model is established. Then, image contrast is introduced as a cost function, and an iterative, modified gradient-based method is used to solve a maximal contrast optimisation problem. The proposed method has a good convergence within a few iterations. The public data provided by the Naval Research Laboratory is utilised to confirm the effectiveness and superiorities of the proposed method.